In recent years, as high-speed data communication and wider bandwidth of communication frequency are desired, in the future, implementation of the Long Term Evolution (LTE) technology using carrier aggregation (CA) is expected. The CA is a method of performing communication by simultaneously using a plurality of carriers called component carriers (CCs). Namely, for example, as illustrated in FIG. 13, communication is simultaneously performed by using a plurality of CCs 11 to 13 each of which has a different frequency.
In FIG. 13, for example, if the CC 11 belongs to a different frequency band to which the CCs 12 and 13 belong, communication is performed by using non-contiguous CCs belonging to different frequency bands. Consequently, in this case, different transmission circuits are provided for at least each frequency band and then amplification or the like is performed by a power amplifier in each of the transmission circuits. In contrast, for example, if the CC 11 and the CCs 12 and 13 belong to the same frequency band, communication is performed by using contiguous or non-contiguous CCs belonging to the same frequency band. In this case, by using a power amplifier common to all of the CCs, it is possible to share a transmission circuit and suppress an increase in the size of a device or the cost.
Patent Document 1: Japanese Laid-open Patent Publication No. 08-213919
Patent Document 2: Japanese Laid-open Patent Publication No. 2009-278225
Patent Document 3: Japanese Laid-open Patent Publication No. 2010-11062
Non-Patent Document 1: 3GPP (3rd Generation Partnership Project), “Feasibility study for Further Advancements for E-UTRA (LTE-Advanced) (Release 11)”, 3GPP TR36.912 v11.0.0, September, 2012
However, if signals of a plurality of CCs are amplified by a single power amplifier, there is a problem in that inter modulation distortion according to the distortion characteristic of the power amplifier is generated. The inter modulation distortion becomes a spurious component of the signal emitted from an antenna and gives an interference with communication performed in a frequency band in which the CCs belong or performed in an adjacent frequency band.
FIG. 14 is a schematic diagram illustrating frequencies of inter modulation distortion generated when signals of two CCs with different frequencies are amplified by a single power amplifier. In FIG. 14, if signals of a CC 1 with a frequency of f0 and a CC2 with a frequency of f1 are amplified by a single power amplifier, in a frequency domain in the vicinity of these CCs, inter modulation distortion is generated in a difference frequency that is an integral multiple of the wave of the frequency of each CC. Namely, for example, in the frequencies (2f1-f0) and (2f0-f1), third-order inter modulation distortions IM3+ and IM3− are generated and, in the frequencies (3f1-2f0) and (3f0-2f1), fifth-order inter modulation distortions IM+5 and IM−5 are generated.
In order to suppress these inter modulation distortions, it is conceivable to increase the power supply voltage supplied to a power amplifier and raise the saturation level of the power amplifier. However, when this countermeasure is taken, electrical power consumption of the power amplifier is increased and thus resulting in an increase in electrical power consumption of the entirety of a wireless communication apparatus.
Furthermore, similar to a case of using CCs with different frequency bands, it is also conceivable to provide a power amplifier for each CC and allow a signal of each CC to be amplified by another power amplifier. However, when this countermeasure is taken, a plurality of power amplifiers is provided in a wireless communication apparatus and thus resulting in an increase in size of a device or the cost.